In the field of optical communication, there is a pressing need to improve the capacity of optical networks and the speed of switching at reasonable cost. These are attended by the related problems of efficient retrofit to existing infrastructure, ease of maintenance, reliability, etc. The physical media of optical fibers used in current generation optical networks have a tremendous as yet untapped reserve capacity. The reasons for this involve various bottlenecks, chief among them, the slow speed of switches for optical data. To switch optical data, either the data on an optically-modulated signal must be converted to electrical modulation and switched by electrical switches, switched by relatively slow state change switches such as electro-optical, or thermo-optical switches, or switched by slow mechanical switches like Micro Electro Mechanical Systems (MEMS). Although the electrical conversion and switching is slow it is still much faster than any technology available today for optical switching. The optical switches are too slow to handle information switching and thus are used only for system management and reconfiguration in which the recovery time that may be tolerated for such application is in the range of microseconds to milliseconds. Some of the switches are much faster than the recovery time of the system and some of them have a time response of 50 ns, but still they are too slow for being used for the purpose of data switching fast enough as to avoid storage, which inevitably involves conversion. Electrical switching is the only technology available today that is capable of acting as a switch in the sense of intelligent switching or packet switching, because of the storage capability. While the switching is intelligent, it is still slow and constitutes a major bottleneck in communication networks. To compensate for the slowness of electronic switching, substantial parallelism must be introduced into the design of switches resulting in high cost, large footprint and power consumption. These limitations are near their upper limits making them very difficult to scale.
Currently, there is no all-optical analog to the network switches used in networks.
In addition to the switching process per se, the process of generating optical signals—the modulation itself—is slow because of the rise and fall times of current optical modulators. As a result, symbols are much longer than need be, thereby limiting the bandwidth to a level substantially below the potential of the optical media.
A technique called Wavelength Division Multiplexing (WDM) and a refinement called, Dense Wavelength Division Multiplexing (DWDM) are currently used to increase the capacity of optical media using current modulation technology. WDM or DWDM methods increase the transmission rate by creating parallel information channels, each channel being defined by a different light frequency. Another method, Time Division Multiplexing (TDM) exists in which multiple data sequences are interleaved in time-division fashion on a common medium.
WDM or DWDM methods increase the transmission rate by using parallel information channels. The information in each optical channel is carried by a different light frequency. The light frequencies of the channels are combined together and are inserted into the input of a single optical fiber. The combined light frequencies at the output of the fiber are separated into different parallel channels, one for each specific light frequency. Although DWM and DWDM have the ability to increase the capacity of a fiber, the number of channels that may be defined has a practical upper limit because of the limited bandwidth of the fiber (optical properties are attuned to a narrow range of frequencies) and because of the ability of the laser sources to contain their energy in very narrow frequency bands.
Even if the line-width of the lasers would be made sufficiently narrow to allow the addition of more channels, the number of channels cannot be increased without limit. Increasing the number of channels results in channel crosstalk. Crosstalk results from nonlinear effects that occur within fiber media when subjected to the intense electrical fields produced when a high channel count is used. In TDM, the bits of several parallel channels at the same light frequency are interleaved in a predetermined periodic order to create a single serial data stream. This method is very effective when using a buffer, which accumulates and compresses the data of several channels into a dense serial data stream of a single channel by reorganizing this data with suitable delays. However the data rate permitted by this method, as well as others, is still limited by the data rate and duty cycle of the modulators or the light sources (DFB and DBR lasers) themselves when direct modulation is used. That is, in direct modulation, the power to the laser is switched on and off. The rate at which this can occur has a physical upper limit due to the relatively long recovery time of the lasers and it produces chromatic dispersions due to broadening of the emitted spectral line of the modulated lasers. This is caused by spontaneous emission, jittering, and shifting of the gain curve of the lasers during the current injection. Where modulation is performed in an indirect manner, by modulators, the lasers are operated in a Continuous Wave (CW) mode and separate modulators perform the modulation of the beam. The modulators are usually made from interference devices such as Mach-Zender's, directional couplers and active half wave-plates combined with polarizers and analyzers. However, an electro-optical device must be activated to modulate the beam and thereby produces phase shifts and polarization changes. Such changes involve the creation and removal of space charges, which change the density of the charge carriers within these electro-optic materials. The formation rate of the space charges is mainly dependent upon the speed and the magnitude of the applied voltage and can be on the order of sub nanoseconds. The charge removal is usually slower and is mainly dependent upon the relaxation time of these materials (lifetime of charge carriers) and can be relatively long. Accordingly, the width of the pulses and the duty cycle of the modulation are dependent limited by the long off-time (latency) of the modulators.
These same rise and fall time limitations impose similar limits on the abilities of switches to direct light along alternative pathways according to routing commands and data. At present, there are two major classes of optical switches. In one class, optical signals are converted to electrical signals, routed and switched conventionally, and optical signals generated anew at the output. As discussed above, the process of conversion is costly and the reduction of switching time is limited since the switching time includes delays due to reading, processing of destinations, reconfiguration delays, device I/O, and regeneration of the optical signals. Thus the switching time is slow requiring many parallel channels to obtain throughput making such switches scale poorly, costly, and otherwise problematic. In optical applications, this class of switches goes by the identifier OEO, which stands for signals medium conversion, from the optical domain to the electrical domain and then back to the optical.
A second class of optical switch, which is often very slow to reconfigure, goes by the identifier OO, which stands for optical-optical, as the signals are maintained thoroughly in the optical domain. In these switches, no conversion of optical signals to electrical signals takes place. Instead, the optical energy is routed by means of some sort of light diversion process such as a switchable mirror. In one system, micromechanical actuators or so-called Micro Electro Mechanical System (MEMS), use electrostatic forces to mechanically move microscopic mirrors in response to electrical routing signals. The speed of such switches is very limited by the slow response of the devices used to perform switching, for example, MEMS mechanism. The result is that no OO switch is capable of packet switching and is only applicable where the granularity of data signals is extremely high, such that the delays required for configuration represent a small fraction of the time required for transmitting. These devices are applicable in the core portions of networks and do not address the bottleneck problems inherent electronic switches.
At present, the highest bit rate being deployed is about 10G bits per second per channel. Higher bit rates designs, such as 40G bit per second per channel, are mainly challenged by developing high bit rate devices, improve optical signal-to-noise ratio and compensate for dispersion. Present high speed 10G bits per second devices are limited by the modulation rate of the modulators, the pulse width that they produce, and the switching time of the electronic switches.
There is a need for reliable mechanisms for exploiting the physical potential of fiber optic media in terms of data rate, switching, and cost.
In optical communication networks there is a need for fast, reliable, and inexpensive systems capable of demultiplexing information. One solution for such a need is provided by Passive Optical Networks (PON) that passively demultiplex the information, by splitters, into multiple customers. Such PON systems have a common use in applications for the last-mile. However such a solution suffers from security problems since every attached PON network customers receives the whole information of all other network customers, regardless of the targeted customer. Accordingly it is desired to produce an inexpensive, simple demultiplexing system in which each customer receives the information in a direct manner and only the information designated specifically to him.
U.S. Pat. No. 5,060,305 entitled “Self Clocked, Self Routed Photonic Switch” filed Oct. 22, 1991 and U.S. Pat. No. 6,160,652 entitled “Optical Address Decoder” filed Dec. 12, 2000, disclose systems and devices for decoding headers in an architecture of sending information by payloads where the destinations of the payloads are encoded in the headers.
The design of the embodiments according to the present invention allows simple direct demultiplexing of the information without the use of headers and payloads. Thus the embodiments of the present invention are simpler, more reliable, faster, and less expensive than the embodiments disclosed by U.S. Pat. Nos. 5,060,305 and 6,160,652.
Accordingly, it is an object of the present invention to provide a passive, inexpensive, and reliable system for direct switching, routing, multiplexing and demultiplexing of information;
Another object of the present invention is to provide passive and fast systems for direct switching, routing, multiplexing and demultiplexing of information in which each customer may receives information directed only to him;
Another object of the present invention is to provide a fast system for direct switching, routing, multiplexing and demultiplexing of information that may include a threshold mechanism and switch the information in a direct manner;
Another object of the present invention is to provide a fast system for direct switching, routing, multiplexing and demultiplexing of information across multiple decoding/switching/routing/demultiplexing layers;
Another object of the present invention is to provide a fast system for direct switching, routing, multiplexing and demultiplexing of information to form cross connection switching and cross-connection boxes for decoding/switching/routing/demultiplexing of information;
Another object of the present invention is to provide a fast system for direct switching, routing, multiplexing and demultiplexing of information that may include a threshold mechanism and in which each customer receives information directed only to him;
Another object of the present invention is to provide fast systems for direct switching, routing, multiplexing and demultiplexing of information including coincidence gates or decoding devices that may be stateless;
Another object of the present invention is to provide coincidence gates that include a summing gate that may be of one of the type of dielectric and metallic beam-splitters, dual gratings, high density gratings, array of radiation guide gratings, Array of Waveguide Gratings (AWG), polarization beam-splitters, directional couplers, and Y-junctions;
Another object of the present invention is to provide coincidence gates that may be produced in any of the media including, open space, radiation guides, fiber optics, wave guides, and planar wave guides fabricated on a chip;
Another object of the present invention is to provide coincidence gates including summing gates that may sum the control and the data signal coherently or non-coherently;
Another object of the present invention is to provide coincidence gates including summing gates that may sum the control and the data signal coherently and have closed loop phase control;
Another object of the present invention is to provide coincidence gates including electrical or optical threshold mechanisms;
Another object of the present invention is to provide coincidence gates that may receive in their inputs control and data signal for a single source or from different sources;
Another object of the present invention is to provide coincidence gates including summing gates that may sum the control and the data signal and have closed loop clock recovery control;
Another object of the present invention is to provide a method and apparatuses to increase the rate of information transmitted using narrow pulse generators and shapers and dense interleaving to produce high dense multiplexing and demultiplexing;
Another object of the present invention is to provide codes with predetermined destinations including at least one control pulse and one data pulse;
Another object of the present invention is to provide codes with predetermined destinations including multiple control pulses;
Another object of the present invention is to provide codes constructed from a plurality of pulses with predetermined destinations including multiple control pulses to route, switch or demultiplex information across multiple routing, switching and demultiplexing layers;
Another object of the present invention is to provide symbol configurations, summing gates, and control pulses for increasing the ratio between coincidence pulses and non-coincidence pulses produced by coincidence gates;
Another object of the present invention is to provide coincidence gates including delay lines;
Another object of the present invention is to provide coincidence gates including variable delay lines;
Another object of the present invention is to provide coincidence gates including delay lines compactly produced on a chip;
Another object of the present invention is to provide optical cross-connection boxes capable of information self routing;
Another object of the present invention is to provide a self routing, switching and demultiplexing mechanism that maintains synchronization;
Another object of the present invention is to provide a self routing, switching and demultiplexing mechanism across DWDM systems that may include multiple switching layers;
Another object of the present invention is to provide embodiments designed to multiplex/demultiplex symbols with predetermined addresses including management of guard band between symbols, and,
Still another object of the present invention is to provide embodiments designed to multiplex/demultiplex symbols with predetermined addresses modulated by any combination of time, phase, and polarization modulation.